High-energy cosmic ray nuclei from tidal disruption events: Origin, survival, and implications

Abstract

Tidal disruption events (TDEs) by supermassive or intermediate mass black holes have been suggested as candidate sources of ultrahigh-energy cosmic rays (UHECRs) and high-energy neutrinos. Motivated by the recent measurements from the Pierre Auger Observatory, which indicates a metalrich cosmic-ray composition at ultrahigh energies, we investigate the fate of UHECR nuclei loaded in TDE jets. First, we consider the production and survival of UHECR nuclei at internal shocks, external forward and reverse shocks, and nonrelativistic winds. Based on the observations of Swift J1644+57, we show that the UHECRs can survive for external reverse and forward shocks, and disk winds. On the other hand, UHECR nuclei are significantly disintegrated in internal shocks, although they could survive for low-luminosity TDE jets. Assuming that UHECR nuclei can survive, we consider implications of different composition models of TDEs. We find that the tidal disruption of main sequence stars or carbon-oxygen white dwarfs does not successfully reproduce UHECR observations, namely the observed composition or spectrum. The observed mean depth of the shower maximum and its deviation could be explained by oxygen-neon-magnesium white dwarfs, although they may be too rare to be the sources of UHECRs.

Tidal Disruptions of White Dwarfs: Theoretical Models and Observational Prospects

“…These authors considered the acceleration of the particles, the reactions that may destroy metal nuclei, the propagation of the particles from the source to the Earth and their detection by the IceCube and Pierre Auger observatories. The general conclusion is that the models can reproduce both the composition and energy spectrum of UHECRs (Zhang et al 2017, note that O-Ne-Mg white dwarfs lead to better agreement). The implied TDE rates range between 0.1 yr −1 Gpc −1 (Biehl et al 2018) and 10 yr −1 Gpc −1 (Alves Batista and Silk 2017) but these are inversely proportional to the baryon loading of the jets (the ratio of proton to photon luminosities) and proportional to the IMBH occupation fraction (see Section 6.3).…”

Open Questions in Cosmic-Ray Research at Ultrahigh Energies

“…It was shown in Farrar and Piran (2014), based on the analysis of the prototypical jetted-TDE Swift J144+57, that jetted-TDEs can likely produce the bulk of observed UHECRs. The expected UHECR output from TDEs was more recently studied in Zhang et al (2017), Dai and Fang (2017), Biehl et al (2018), and Guépin et al (2018) in the internal shock model. The above analyses conclude that given the relatively low inferred rate of jetted TDEs based on Swift data, whether the energy-budget constraint is satisfied depends intricately on the relation between the TDE radiative luminosity and UHECR luminosity.…”

“…Intermediate-mass black holes may also tidally disrupt stars. Depending on the combination of masses of both objects, tidal squeezing may trigger nuclear burning in the core of white dwarfs, leading to a supernova and potentially accelerating cosmic rays to ultrahigh energies (Alves Batista and Silk, 2017;Zhang et al, 2017;Guépin et al, 2018).…”

Cosmogenic photon and neutrino fluxes in the Auger era

“…Refs. [37][38][39] have also suggested that jetted TDEs may lead to hard spectra.Even if hard spectra production were achieved at each source, it is likely that the overall diffuse UHECR spectrum softens through the integration over the population of sources. Indeed, sources with milder characteristics, which will produce lower-energy particles, are more numerous, and the distribution of their parameters will naturally soften the spectrum [40,41].…”